Cardable fiber blend and a moldable fiber batt and the process for making a moldable fiber batt

ABSTRACT

The present invention provides a cardable fiber blend which forms a moldable fiber batt, the blend comprising fibers having a modulus of 550 g/denier or more with fibers of a thermoplastic polymer wherein the high modulus polymer fibers are all uncrimped fibers or a mixture of crimped and uncrimped fibers. The moldable batt is useful in making speaker cones.

This is a division of application Ser. No. 09/401,695, filed Sep. 23,1999, now abandoned.

BACKGROUND OF INVENTION

Methods for forming fiber batts require the use crimped fibers becauseuncrimped fibers are very difficult if not impossible to process throughtextile equipment. In some applications such as speaker cones, highmodulus fibers are used in making the cone because these fibers stiffenand improve sound reproduction. Before the present invention, it wasnecessary to crimp these high modulus fibers before they could beprocessed to form batts or felts. In the crimping process these stifffibers are broken and damaged. Fiber is also lost or wasted contributingto an increased in cost for such crimped fibers. Even if no fiber werelost or damaged in crimping, the need for this step, alone, adds bothprocessing time and costs in the production of batts and the productsmade from these batts.

Speaker cones are generally made from a paper or from a felt. Papers arenon-woven webs produced by a wet lay process on paper machines, whilenon-woven felts are produced from fiber batts that are needled together.

U.S. Pat. No. 4,112,168 teaches a speaker cone produced by impregnatinga fiber web with a resin solution, evaporating the solvent to produce anon-woven fabric and then simultaneously laminating to this fabric a gastight film while molding the fabric into the speaker cone.

In another patent, U.S. Pat. No. 4,359,132, a speaker cone is producedby forming a needled felt from ptextile fibers and polypropylene textilefibers. Textile fibers are crimped fibers that allow easy processingthrough textile equipment.

British Patent 2 037 122 B teaches a speaker cone made of a paper formedon a paper machine from stiff fibers such as p-aramid or carbon fibers.

SUMMARY OF INVENTION

An object of the present invention is to provide a easily moldable battusing uncrimped high modulus polymer fibers. Such a bat may be moldedinto high quality speaker cones.

Another object in the present invention is to provide a cardable fiberblend from which the moldable batt may be formed.

Another object of the present invention is to provide a process forproducing a fiber batt that does not require crimped high modulus fiber.

Another object of the present invention is to provide a high qualityspeaker cone and a process for making this speaker cone.

DETAILED DESCRIPTION

The present invention provides an intimate, cardable fiber blend thatmay be formed into a batt. This fiber batt is particularly useful inmaking speaker cones.

As used herein, the term high modulus polymer fiber means a fiber thathas a modulus of 550 g/denier or more. High modulus polymer fibers thatare particular useful in the present invention include p-aramid andaromatic polyester fibers. Such fibers having a modulus of 750 g/denieror more are particularly preferred. In processing the uncrimped highmodulus fibers, the rate of carding may be increased by mixing into theuncrimped high modulus fiber an amount of crimped high modulus fiber.

When speaker cones are the desired product, it is recommended that theamount of crimped high modulus fiber present in a mixture with uncrimpedhigh modulus fiber be less than 50% of the total weight of the mixtureof crimped and uncrimped high modulus fiber.

It is believed that the use of uncrimped high modulus fiber is ofparticular advantage for speaker cones. The presence of uncrimped highmodulus fiber produces a cone that, at least when rated subjectively,produces an improved sound reproduction, particularly of the humanvoice. Thus it is most desirable to use all uncrimped high modulusfiber. The mixing of crimped and uncrimped high modulus fiber asdescribed above allows one to balance sound reproduction quality andrate of carding while realizing benefits from the use of uncrimped highmodulus fiber in the cone.

The cardable fiber blend and the fiber batt of the present invention maybe used for other purposes than making a speaker cone or other moldedproduct. The batt itself may be used in insulation or for padding.

Since the batt of the present invention contains thermoplastic polymerfiber, the batt may be designed through polymer fiber selection to beeasily moldable over a range of temperatures, or to be stable over arange of temperatures. For a moldable fiber batt, polyolefin, polyesterand polyphenylene sulfide fibers are useful. Polypropylene fibers aremost desirable for use in making speaker cones.

The present invention provides a process for making a fiber batt using ablend of crimped and uncrimped fibers. Synthetic polymer fibers arecrimped so that they process as natural fibers and can be processed toform batts, webs and fabrics using textile equipment. There is theadvantage of eliminating a process step, if uncrimped synthetic polymerfibers could be directly formed into a web or batt.

The inventor in the present invention has found that by combiningthermoplastic crimped polymer fibers and uncrimped high modulus polymerfibers, a combination of fibers is formed that can be processed bytextile equipment to form a batt or web. Even when a high concentrationof the uncrimped fiber is present, the fiber blend of the presentinvention can be processed using, for example, a Rando Webber or otherequipment for forming a web or batt.

In the present process the thermoplastic polymer fibers and the highmodulus fibers are opened. Each fiber type may be opened separately andthen combined to feed the webber or card, or the two types of fibers canbe first blended together, then opened and the opened blend is then fedto the webber or card.

Card rates can be increased by using a mixture of uncrimped and crimpedhigh modulus fibers along with the thermoplastic polymer fibers.Generally for blends of the present invention, it is recommended thatthe amount of crimped high modulus fiber be present in an amount of notmore than 50% of the total weight of the mixture of crimped anduncrimped high modulus fiber.

The weight range preferred for batts for the present invention is from0.5 to about 7 oz./yd². Batts may be made at a desired weight by formingthat weight directly at the card or webber, or they may be made bylaminating lighter weight batts together to give the desired weight.This latter method is useful in molding speaker cones since singlethickness batts tend to wrinkle in the molding process. Also inproducing batts for molding, it is preferred that the batt be of lowdensity. To achieve a low density batt, it is preferred to produce thebatt using blower air-ducted or vacuum air duct process equipment, forexample, a Rando Webber.

In selecting fibers for the present process, it is preferred that thatthe high modulus fibers are selected from the group consisting ofp-aramid, aromatic polyester, poly phenylene sulfide and aromaticpolyimide fibers and that the crimped thermoplastic fibers arepolyolefin or polyester fibers or a mixture of these fibers. It isparticularly desirable that the high modulus polymer fibers are alluncrimped p-aramid fibers and the thermoplastic polymer fibers arepolypropylene.

The batt of the present invention may be molded into desired shapes ifafter step (c), the batt is molded in a high temperature, high pressuremold.

If one desires to mold speaker cones from the batts of the presentinvention, high quality speaker cones may be made using the followingimproved process: (a) blending together high modulus polymer fibershaving a modulus of 550 g/denier or more with fibers of a thermoplasticpolymer wherein the high modulus polymer fibers are all uncrimpedfibers,(b) passing the blend through a device to open the fibers, (c)forming the fibers into a batt,(d) heating a mold to about 200° F. andplacing the batt in the mold to form a speaker cone,(e) applying apressure of from 5 to 20 tons to the mold and heating the mold to about380° F., (f) allowing the mold to cool to about 200 ° F. before openingthe mold to remove the speaker cone.

In this improved process it is desirable that the high modulus polymerfibers are selected from the group consisting of p-aramid, aromaticpolyester, poly phenylene sulfide and aromatic polyimide fibers and thatthe crimped thermoplastic fibers are polyolefin or polyester fibers or amixture of these fibers. It is also desirable that the batt formedcontains from about 30% to about 70% by weight of high modulus polymerfibers and from about 70% to about 30% by weight crimped thermoplasticfibers. Also in this process during molding the batt a polyolefin filmcan be laminated to the batt. For speaker cones it is particularlydesirable that the high modulus fibers are all uncrimped p-aramid fibersand the thermoplastic fiber is polypropylene.

In the molding process the speaker cone may be colored by selecting thefibers, both the thermoplastic polymer and the high modulus fibers, fromfibers either natural colored thermoplastic polymer fibers, naturalcolored high modulus polymer fibers, colored thermoplastic polymerfibers and colored high modulus polymer fibers. Combinations of thenatural colored p-aramid fiber, for example which is yellow with eithercolored or natural colored polypropylene fibers all some latitude informulation a desired hue and shade. A second method by which thespeaker cones of the present invention may be colored is to laminate athin film of the thermoplastic polymer colored to the desired hue andshade to the speaker cone surface during the molding step. This secondmethod of producing a color offers a wide possibility of both hue andshade in a speaker cone product.

The present invention is illustrated by the following non-limitingexamples.

EXAMPLE 1

Uncrimped KEVLAR 49 brand poly p-phenylene terepthalamide fiber producedby E. I. du Pont de Nemours and Company of Wilmington, Del., and havinga nominal tensile modulus 885 gms/denier, a nominal breaking tenacity23.6 gms/denier in ¼″ cut length and a 1.5 denier was preopened by usinga vacuum air duct system. (KEVLAR is a trademark of E. I. du Pont deNemours and Company).

Crimped polypropylene fibers having a 1.5″ cut length and 1.5 denierwere pre-opened by passing them through the Rando Opener. These twofibers were blended in a ratio of 50/50 by weight using the vacuum airduct system. Blends were processed through the Rando Opener three timesfollowed by running two times through the Rando Webber to producenon-woven batts. These webs were rolled using cellophane or paper as theliner. Batts of the following weights were produced 2.5, 3.5 and 4.5oz./yd². In several cases steam was used in the Rando Webber forimproved processing.

The webs or batts were then die cut or layered and die cut into piecesof about 6″ diameter for molding into cones. The desired mold wasinstalled into a high temperature press and heated using band heaters to380° F. The die cut sample was placed between the two halves of themolds, and the press was closed to a molding pressure of from 5 to 20tons. After about 20 seconds, the cold water was circulated to cool themold to about 150° F. The press was opened and the part removed.

These cones were assembled into speakers and compared with paper andpolypropylene cones. In key listening tests, these cones providedsuperior acoustic performance particularly higher sensitivity and lowerdistortion than the controls.

EXAMPLE 2

Uncrimped KEVLAR 149 brand poly pterephthalamide fibers having a tensilemodulus 1000 gms/denier, breaking tenacity 21 gms/denier and cut length¼″ were blended with polypropylene fibers and formed into a battaccording to Example 1. These batts were also molded into cones.

The cones were yellow in color, because of the natural color of K149 andthe natural white color of the polypropylene fibers.

EXAMPLE 3

Uncrimped natural yellow color KEVLAR 149 brand fibers were blended withblack color polypropylene, resulting in a greenish color batt. This battwas molded into cones that have marble green look to them.

EXAMPLE 4

The dark blue colored KEVLAR 49 brand fibers were blended with blackpolypropylene fibers, resulting in a dark bluish black batt. This batt,together with layers of black polypropylene placed on each face of thebatt, were placed in the mold and processed. Darker colored cones wereproduced.

EXAMPLE 5

A speaker cone was molded in the improved process of the presentinvention by heat the mold to 200° F., placing batt made according toExample 1 between the molds and closing the press and applying 10-20tons pressure. The mold was then heated to 380° F.; and after a holdtime of about 10 minutes, the mold was cooled down to about 200° F. Thepress was then opened and the cone removed. The quality and uniformityof this cone was very high because of intimate blending of polypropyleneand p-aramid fibers in the formation of the batt in this moldingprocess.

What is claimed is:
 1. A speaker cone formed by (a) blending togetherhigh modulus polymer fibers having a modulus of 550 g/denier or morewith fibers of a crimped thermoplastic polymer wherein the high moduluspolymer fibers are all uncrimped fibers or a mixture of crimped anduncrimped fibers, (b) passing the blend through a device to open thefibers, and (c) forming the fibers into a batt, wherein after step (c),the batt is molded in a high temperature, high pressure mold and whereinthe high modulus polymer fibers are selected from the group consistingof p-aramid and aromatic polyester fibers.